As well known in the art, an acoustic guitar has (1) several tensioned strings that, when vibrated, produce sounds of desired tone and frequency, and (2) a resonance cavity positioned proximate to the strings to modify and amplify the sounds. In comparison, an electric guitar typically lacks a resonance cavity and relies, instead, upon electrical amplification and modification of the strings' sound. Within this disclosure, the term “guitar” is used to refer generally to an instrument having a resonating cavity, including the above-defined acoustic guitars and electric/acoustical guitars that use electrical circuitry to modify sound from the resonance cavity.
For several centuries, instrument builders have constructed guitars using the same basic design. In particular, a guitar has a body section with a smaller upper bout and a larger lower bout that are separated by a narrower waist area. The body is constructed with a braced top panel and back panel, as well as bent side ribs connecting the top and back panels. The top has a sound hole, usually a round opening near the center of the top. The design also has a cantilevered arm, known as a neck, that extends from the body at a neutral position of the upper bout. Strings attach to a distal end of the neck, called a head. The neck is typically fretted to a musical scale with a fret board attached over the neck and body and ending proximate to the sound hole. The top holds a coupling device, or bridge, at which the strings attach to the top. In this configuration, the strings extend from the distal end of the neck, over the fret board and sound hole, and attach to the bridge to create a medium through which the acoustic qualities of the design can be exploited for the purpose of making music. For example, the body forms the resonance cavity to modify and amplify the strings' sounds. The body can be modified as necessary to achieve desired tonal qualities.
The strings are kept at relatively high tensions, and accordingly, they apply a strong compressive force between the neck and the bridge. However, the above-described general guitar structure has an inherent weakness created by the positioning of a sound hole intermediary to the ends of the strings, where compression force can compress the cantilever action of the neck and cause the formation of a frequency mode in the neck. This structural defect dampens string energy by compromising the stability of the locations to which the strings are attached. The resulting flexibility further causes long-term structural weakness. The sound hole lacks sufficient strength to resist the string tension and deforms over a long period of time. In fact, the sound hole of guitars may shift measurably in shape from a round circle to an oval. The deformation of the sound hole causes shifts the placement of the neck, altering the neck's alignment relative to the body and adversely effecting the instrument's sound qualities.
In order to secure the guitar structure under the compressive force from the strings, the body is generally reinforced according to several different methodologies known in the art. For example, it is known to increase the strength of the guitar body by increasing the strength of the side ribs and/or back through the use of thicker, laminated sheets of materials. Guitar builders have also used laminated side ribs and back to alter sound qualities of the instrument. However, the use of thick, laminated materials makes the guitar undesirably heavy. For example, a laminated side typically has two, three or even 4 plies, adding considerable mass to the instrument. A guitar assembly with non-laminated sides requires a top and back liner, and guitar assembly having laminated sides further requires reinforcing strips or linings glued along the top and the back. Increasing the number of parts makes the guitar relatively more expensive to build because added parts requires added steps in construction and more labor is required.
One known guitar assembly that uses laminated sides is the guitar design of Greg Smallman, a well-known Australian guitar builder. As illustrated in FIG. 1, this design features a heavy, laminated structure that fits inside a surrounding side assembly and a soundboard that attaches to the composite structure to form the top of the guitar body. The composite structure has cutouts to redo weight and to modify the guitar's tonal qualities, including a large cutout in the larger, lower bout of the laminated structure that unencumbers the relatively flexible soundboard from the more solid laminated structure and creates a functional area in which the soundboard resonates to amplify string vibrations. The guitar assembly is further reinforced by gluing two heavy beams at angles between the narrow waist air of the guitar and the bottom end of the instrument at the lower bout center. These beams stabilize the guitar assembly structure to protect the necessarily thin and fragile soundboard from a distortion or movement in the composite side assembly after the instrument is fully loaded with string tension. The design contains many novel innovations to traditional designs to improve the guitar's tonal qualities. For example, the guitar's thin soundboard that is very thin at a functional air near the lateral region where the top connects to the side. This thinness loosens the soundboard to allow it to vibrate more freely relative to the side pieces, creating a guitar having greater volume and tone. However, this weakness of the soundboard requires great reinforcement of the guitar assembly so that the guitar assembly may withstand the compression forces of the strings. Otherwise, the leveraging of the guitar's cantilevered neck distorts the body structure under string tension, potentially distorting or fracturing the soundboard. A guitar produced using this design has improved sound quality over traditional guitars. However, this design for a guitar has several limitations. For example, the laminated structure of the soundboard covers so much area that the sound board limits and closes off the available space required for most standard soundboard reinforcement design, or bracing patterns. The reduced area of the laminated soundboard also requires a thinner top perimeter to loosen the soundboard, as needed for increase amplitude. Another limitation of the design is that the reinforcement beams, describe above, only add support for the lower bout of the instrument. Furthermore, the use of the laminated structures to achieve structural integrity makes the resulting instrument very heavy. As a result, there exists a current need for an improved guitar body in which the soundboard is allowed to resonate as needed to produce desirable sound quality without incurring these limitations.
In another known methodologies to reinforce the guitar body, a reinforcing counter-leveraging member is positioned through the guitar body at a midpoint between the top and back. For example, U.S. Pat. No. 3,435,721, issued to Dopera, describes a guitar assembly having an integrated neck extension that extends through the body and is counter-positioned by jacks against the guitar back. Similarly, the Larson Brothers, who produced and marketed guitars and other string instruments under many different names in the first half of the 20th century, installed a reinforcing metal tube through the body, halfway between the back and top. The metal tube was anchored to structural blocks at the neck and a butt end of the guitar body, opposing the neck. However, in the methodologies taught by Dopera and the Larson brothers, the placement of a counter leveraging member through the body at a mid point between the top and back is geometrically deficient to protect the sound hole from load because the leverage force of the neck fulcrums at the plane of the top and is most efficiently countered there.
Furthermore, all of the above-described reinforcement methods are either deficient mechanically, lacking well planned integration of parts, or are complex structures that are difficult to build. In addition, known design for reinforcing a guitar body do not directly addresses and remedy the distortion created by the loading of the neck on the side assembly as an independent unit leaving the top structure to carry to load in tandom with the side structure. Also, none of the known designs for reinforcing a guitar body adequately address the needs of the top's primary ampliphonic function. Therefore, there exists a current need for an improved methodology for reinforcing the structure of the guitar body.